The internal combustion engine has been the work horse of the modern world for over 100 years. From its conception, misfiring cylinders have been a concern for users. A “misfire” is a lack of complete combustion in one or more cylinders in an engine and may be caused by a variety of sources (for example, a faulty spark plug). Early on, the use of one-cylinder engines meant that engine misfire detection was not needed. However, with the advent of multiple-cylinder engines, a way of detecting which cylinder of a multi-cylinder engine was misfiring was needed. Ways of detecting misfires have been introduced over the many years that the internal combustion engine has been in service. However, the problem with these prior methods is the difficulty of use and lack of accuracy of the testing devices.
During a misfire, a pressure pulse is generated in the exhaust stream, and the pulse moves from the atmospheric pressure back into the exhaust system (referred to as a “negative pulse”). This negative pulse is an indication of a cylinder that has not completed the combustion event within the cylinder. There have been previous attempts to detect a misfire from exhaust pulsations. The Senx™ FirstLook™ probe is one such device. The Senx™ probe detects exhaust pulses and generates a voltage that can be viewed on an oscilloscope. The problem with this and other such devices is the resonant frequency that is created in the exhaust system. Such sensors produce a waveform that moves with each of the fluctuating exhaust pulses. These fluctuating pulses are not desirable when detecting a misfire from the exhaust system. What is needed is a way to filter out these fluctuating pulses and amplify the negative pulse.